1. Field of the Invention
The invention relates to cable tv networks (CATV), and more particularly to apparatus for transmitting return communications in a two-way system.
Common one-way CATV systems have the disadvantage that they are not interactive. The customer's only options are to select one of the channels which are available on the service drop cable, or to place a telephone call to a control center to enable or alter a service; for example, to enable a pay-per-view channel.
Although they are not yet widely available, Full Service Networks (FSN) are proposed which provide a much higher bandwidth for information channels from the network node, and also allow return information over one or more channels having a much greater bandwidth than is possible over a standard telephone connection.
2. Description of the Prior Art
CATV systems commonly use coaxial cable to provide a plurality of services over different carrier frequencies to the subscriber's premises. Although early CATV systems carried only a relatively small number of channels, it is now common that up to 80 or even more channels are provided. FSN carrier frequencies for the service transmissions to a subscriber multimedia device may range typically in a band from 54 to 750 Mhz.
One-way CATV systems customarily use coaxial cable for distribution of service signals within a subscriber's premises. However, some FSN systems will offer telephone service over the same CATV service drop from the tap (usually in the street) to the premises entry point. To minimize costs, it is desirable that these and other services utilize existing wiring within the house or office wherever possible. Therefore some of the wiring which is functionally part of a subscriber premises local bus (referred to hereinafter in the specification and claims as SPLB) because it is connected, directly or indirectly, to the entry point, will be unshielded twisted pair, which is susceptible to picking up electromagnetic noise or signals at RF frequencies from other devices on the premises.
Wherever two-way systems are currently provided, the return systems typically operate in an RF band of 5 to 42 Mhz, with the carrier frequencies being generated in the various sets which are connected to the SPLB. These return transmissions are then simply passed through any protective interconnect device between the SPLB and the cable drop, and then along the drop and the cable on the street.
Two-way systems as described above offer the possibility of maximizing band usage on the transmission cable between the head end or transmission node and the user site, such as the line tap adjacent the user's building. However, the quality of transmission is sometimes degraded by impulse noise funneling into the system via the SPLB. Such noise often is due to CB transmitters, ham radios, or other electrical noise originating in residences and industrial sites. These noise sources tend to be particularly strong at the lower frequencies used for return transmissions.